1. Field of the Invention
This invention relates to high temperature heating vessels, and in particular, to a heat and wear resistant lid for a glass melting furnace.
2a. Technical Considerations
One type of glass melting process entails depositing pulverulent batch material into a pool of molten glass maintained within a tank-type melting furnace and applying thermal energy until the materials are melted into the pool of molten glass. The melting furnace conventionally contains a relatively large volume of molten glass so as to provide sufficient residence time for currents in the molten glass to effect some degree of homogenization before the glass is discharged to a forming operation. These recirculating flows in a tank-type melter may result in inefficient use of thermal energy. Conventional overhead radiant heating is inefficient in that only a portion of its radiant energy is directed towards the material to be melted.
As an alternative to conventional tank-type glass melting furnaces, as described above, U.S. Pat. No. 4,381,934 to Kunkle and Matesa discloses an intensified batch liquefaction process in which large volumes of batch are efficiently liquified in a relatively small liquefaction vessel. This type of process, particularly when using intensified heat sources, produces relatively small volumes of high temperature exhaust gas. The heat from this exhaust gas may be recovered and used to directly heat a batch stream of materials feeding the liquefaction vessel so as to improve the overall efficiency of the process.
In a glass batch melting process as taught in U.S. Pat. No. 4,381,934, the heating process may cause portions of the batch material being heated to vaporize. These vapors are corrosive and combine with the high temperature exhaust gas from heating burners that circulates throughout the vessel to form a high temperature, corrosive gas. In addition, particulate matter from the batch material may become entrained in the exhaust gas stream. These entrained particulates have an abrasive action which, when combined with the high temperature, corrosive gas stream will corrode and erode unprotected, exposed surfaces within the heating vessel.
Due to the corrosive effects of the exhaust gas stream within the vessel which are accelerated by the high temperatures as well as any abrasive or erosive effects from the entrained particulates, exposed surfaces within the vessel, and in particular the vessel lid, must be designed to withstand these deleterious conditions so as to reduce maintenance and/or replacement of the lid that is necessitated by excessive wear along its inner surface. It would be advantageous to have a wear resistant lid design that could withstand such operating conditions and provide a prolonged operating life.
2b. Patents of Interest
U.S. Pat. No. 3,765,858 to Settino teaches a method of roll forming a ribbon of glass at high temperatures by bringing the glass, while still molten, into contact with a roll faced with an iron-based alloy which includes, among other components, 5.0 to 5.8 percent chromium by weight. The patent discloses other roll configurations wherein the rolls are provided with a surface of AISI type 410 or 420 stainless steel.
U.S. Pat. No. 4,216,348 to Greenberger teaches a water cooled roof panel assembly for an electric arc furnace. Copper sheets are brazed to a steel backing having integral ducts to circulate cooling fluid through the panel. An outer ring around the roof assembly acts as both a water source and drain for the panels.
U.S. Pat. Nos. 4,182,610 to Mizuno et al. and 4,197,422 to Fuchs et al. teach a water cooled furnace cover having a plurality of cooling boxes or jackets that provide a ducting arrangement such that coolant may circulate through the cooling boxes to cool the furnace cover. In Mizuno et al., fin-like members extend from the lower surface of the furnace cover so that a slag layer may adhere to the fins to form a heat insulating layer. In Fuchs et al., a protective layer of refractory material is disposed on the underside of the cooling boxes to provide additional thermal protection for the cover.
U.S. Pat. No. 4,453,253 to Lauria et al. teaches a wall and roof construction for electric arc furnaces that are made of graphite blocks with removably attached fluid cooled panels. The panels contain conduits for circulating a cooling fluid along the exterior surface of the block to cool it.